There are various ways of manufacturing a wind turbine rotor blade. For example, in EP 1 310 351 A1 a method for making a windmill blade is disclosed, whereby problems with glue joints and with exposure of the workers to environmentally hazardous substances are avoided. In FIG. 6 of EP 1 310 351 A1 two parts of a mould core are placed on an inner layer of fibre material. A shear web is placed between the two parts of the mould core. On both sides of the shear web fibre material can be placed. The fibre material may be placed around the shear web and to some extent across the inner layer of fibre material as well as across the core part.
For one embodiment of the manufacturing method, the web and the glass fibre surrounding it is build up on a position remote to the mould and then subsequently lifted to its position in the mould.
In order to decrease the weight of the blades, PET-foam (PET: polyethylene terephthalate) can be used as web material. However this requires—as the packing procedure of the fibre material is done today—that the web has to carry the weight of the glass fibre material until it is placed in the mould as described above. However the use of PET-foam induces deformations in the casted web as its mechanical properties are different to plywood such as it has a lesser stiffness and therefore deforms under the weight of the fibre material.